Organic electroluminescent device with enhanced light emission

ABSTRACT

An organic electroluminescent device is provided which includes a colored polarizer to reduce power consumption requirements for desired levels of brightness. The organic electroluminescent device includes a substrate, an anode electrode layer, an organic layer, a cathode electrode layer, and a colored polarizer provided on a surface of the substrate opposite a surface of the substrate on which the anode electrode layer is formed such that the colored polarizer polarizes light incident from the outside. The colored polarizer increases transmission of a given color of light based on the color(s) included in the polarizer to thereby decrease total current required by the organic electroluminescent device.

This application claims priority to Korean Patent Application No.2005-76384 filed in Korea on Aug. 18, 2005, the entirety of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a display device, and more particularly, anorganic electroluminescent device.

2. Description of the Related Art

In an organic electroluminescent device, the brightness characteristicsof the red pixels R are typically inferior to those of the green G andblue B pixels. Thus, more current should be applied the R pixels inorder to emit the same level of brightness as the G and B pixels. Forexample, to emit 100 candela of brightness, 10 mA current should beapplied to the G pixel, and 20 mA current should be applied to the Bpixel. However, a 70 mA current should be applied to the R pixel inorder to emit 100 cadela of brightness. Thus, a great deal of current isrequired to emit the same level of brightness from the R, G and Bpixels, thereby increasing the power consumption of the organicelectroluminescent device. Therefore, there is a need to decrease powerconsumption requirements of organic electroluminescent devices whilemaintaining desired display characteristics

SUMMARY OF THE INVENTION

An object of the invention is to solve at least the above problemsand/or disadvantages and to provide at least the advantages describedhereinafter.

It is an object of the invention to minimize power consumption.

Another object is to decrease total current required when the organicelectroluminescent device emits.

Another object of the invention is to provide an organicelectroluminescent device which decreases current required at the timeof emitting of the organic electroluminescent device by using a coloredpolarizer according to brightness characteristics of R, G and B pixels.

To achieve these objects, in whole or in part, as embodied and broadlydescribed herein, an organic electroluminescent device in accordancewith an embodiment of the invention includes a substrate, an anodeelectrode layer, an organic layer, a cathode electrode layer and acolored polarizer, the colored polarizer polarizing light incident fromthe outside being adhered to a surface of the substrate contrary to anupper side of the substrate on which the anode electrode layer isformed.

As described above, the organic electroluminescent device in accordancewith embodiments of the present invention may minimize power consumptionby decreasing total current required when the organic electroluminescentdevice emits.

In addition, the organic electroluminescent device in accordance withembodiments of the invention uses a colored polarizer according tobrightness characteristics of R, G and B pixels, thereby decreasingcurrent required when the organic electroluminescent device emits.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objects and advantages of the invention may be realizedand attained as particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in detail with reference to thefollowing drawings in which like reference numerals refer to likeelements wherein:

FIG. 1A is a sectional view of an organic electroluminescent device inaccordance with an embodiment of the invention;

FIG. 1B is an exemplary sectional view of an organic emitting layer of eorganic electroluminescent device shown in FIG. 2A; and

FIG. 2 is a bar graph comparing current required to emit a given levelof brightness using different types of polarizers.

DESCRIPTION OF EMBODIMENTS AND/OR BEST MODE

The organic electroluminescent device 200 shown in FIG. 1A includes asubstrate 202, an anode electrode layer 204, an organic layer 206, acathode electrode layer 208 and a colored polarizer 210. The anodeelectrode layer 204 may be provided on the substrate 202 by, forexample, a deposition type process.

The organic layer 206 may be provided on the anode electrode layer 204by, for example, a deposition type process, and may include a holeinjection layer (HIL), a hole transporting layer (HTL), an emittinglayer (EML), an electron transporting layer (ETL), and an electroninjection layer (EIL), as shown in FIG. 1B. These layers of the organiclayer 206 may be formed in the sequence shown in FIG. 1B, however, otherarrangements may also be appropriate. The cathode electrode layer 208may be formed from a metal such as, for example, aluminum (Al), and maybe provided on the organic layer 206 by, for example, a deposition typeprocess.

Hereinafter, an emission process associated with the organicelectroluminescent device 200 will be described in detail.

The anode electrode layer 204 provides holes to the HIL of the organicemitting layer 206 if a certain positive voltage is applied thereto. Thecathode electrode layer 208 provides electrons to the EIL of the organicemitting layer 206 if a certain negative voltage is applied thereto. TheHIL smoothly injects the holes provided from the anode electrode layer204 to the HTL, and the EIL smoothly injects the electrons provided fromthe cathode electrode layer 208 to the ETL. The HTL then transports theholes received from the HIL into the EML, and the ETL transports theelectrons received from the EIL into the EML. The transported holes andelectrons are recombined in the EML, and a light having a predeterminedwavelength is from the EML of the organic emitting layer 206 to theoutside through the substrate 202 and the polarizer 210.

The polarizer 210 may be provided on a surface of the substrate 202which is opposite an upper surface of the substrate 202 on which theanode electrode layer 204 is provided, that is, a lower surface of thesubstrate 202, as shown in FIG. 1A. However, other positions for thepolarizer 210 may also be appropriate. For example, the polarizer 210may be provided between the substrate 202 and the anode electrode layer204. The polarizer 210 transmits the light emitted by EML with a giventransmissivity, and may also intercept light reflected from the cathodeelectrode layer 208, thereby improving contrast in the image displayedby the organic electroluminescent device 200.

The polarizer 210 in accordance with an embodiment of the invention mayinclude a red-colored substance. If the brightness characteristics ofthe R pixel are inferior to those of the G and B pixels, then morecurrent would have to be applied to the R to yield the same brightness.However, by using a colored polarizer 210 which includes a red-coloredsubstance, emission of red color from the R pixels may be improved whencompared to a regular polarizer without applying additional current tothe R pixels.

Thus, an organic electroluminescent device 200 which includes this typeof colored polarizer 210, in accordance with an embodiment of theinvention, can emit red light at the same level of brightness as thegreen and blue light without increased power consumption. Thus, powerconsumption requirements of the R pixel for a given level of brightnessmay be decreased.

FIG. 2 is a bar graph comparing current required to emit a given levelof brightness by R, G and B pixels using different types of polarizers.As shown in FIG. 2, to emit 100 candela of brightness in an organicelectroluminescent device 200 as shown in FIGS. 1A-B, using a coloredpolarizer 210 in accordance with an embodiment of the invention, only 40mA of current is supplied to the R pixel to achieve the desired 100candela of brightness. Thus, compared to the regular polarizer, powerconsumption requirements of the R pixel may be decreased by about 30 mA.

This may cause the current consumed by the G and B pixels to be slightlyincreased due to the red-color included in the colored polarizer 210,and so more current may need to be applied to emit acceptable levels ofgreen light or blue light. However, as the G and B pixels have higherbrightness characteristics, the G and B pixels can emit the same levelof brightness as the R pixel with only a small amount of additionalcurrent.

For example, in order to emit 100 candela of brightness from the organicelectroluminescent device 200 in accordance with an embodiment of theinvention, the G pixel needs approximately 15 mA of current, which isonly about 5 mA more than the current required by an electroluminescentdevice using a regular polarizer. Likewise, to emit 100 candela ofbrightness, the B pixel needs approximately 25 mA of current, which isonly about 5 mA more than the current required by the device using aregular polarizer. Accordingly, to emit 100 candela of brightness, thetotal current required by an organic electroluminescent device inaccordance with an embodiment of the invention is approximately 80 mA,which is approximately 20 mA less than the current required by a deviceusing a regular polarizer, whose total required current is approximately100 mA.

The relationship between the levels of current which should be suppliedto each of the R, G and B pixels in order to maintain a given level ofbrightness, such as, for example, the 100 candela of brightness shown mFIG. 2, is substantially linear. Thus, a ratio may be applied toapproximate the relative levels of current required to maintain aparticular level of brightness. For example, based on the exemplary datashown in FIG. 2, a ratio of the current required by the R pixel (70 mA)to the current required by the G pixel (15 mA) is approximately 2.6,compared to a ratio of 7 when using the regular polarizer Likewise, aratio of the current required by the R pixel (70 mA) to the currentrequired by the B (25 mA) pixel is approximately 1.6, compared to aratio of 3.5 when using the regular polarizer.

Thus, power consumption in accordance with an embodiment of theinvention may be decreased for a given level of brightness by using apolarizer as described above and applying appropriate levels of current.Additionally, by controlling of a concentration of a red-coloredsubstance in a colored polarizer of an organic electroluminescent devicein accordance with an embodiment of the invention, power consumed byeach of the R, G and B pixels may be controlled.

Additionally, the colored polarizer 210 may include substances havinggreen-color, or blue-color. That is, the color of the polarizer 210 canbe controlled based on desired brightness characteristics or mainemitting color of an organic electroluminescent device in accordancewith an embodiment of the invention.

The foregoing embodiments and advantages are merely exemplary and arenot to be construed as limiting the present invention. The presentteaching can be readily applied to other types of apparatuses. Theelectroluminescent device of the present invention may be used in orformed as flexible display for electronic books, newspapers, magazines,etc., different types of portable devices, e.g., handsets, MP3 players,notebook computers, etc., audio applications, navigation applications,televisions, monitors, or other types of devices using a display, eithermonochrome or color. The description of the present invention isintended to be illustrative, and not to limit the scope of the claims.Many alternatives, modifications, and variations will be apparent tothose skilled in the art. In the claims, means-plus-function clauses areintended to cover the structures described herein as performing therecited function and not only structural equivalents but also equivalentstructures.

1-10. (canceled)
 11. A method of operating an electroluminescent device,comprising: providing a first current to produce a corresponding firstcolor of light; providing a second current to produce a correspondingsecond color of light; and providing a third current to produce acorresponding third color of light, wherein a magnitude of the firstcurrent is less than approximately 7 times a magnitude of the secondcurrent, and less than approximately 3.5 times a magnitude of the thirdcurrent.
 12. The method of claim 11, wherein the magnitude of the firstcurrent is between approximately 2 and 7 times the magnitude of thesecond current.
 13. The method of claim 12, wherein the magnitude of thefirst current is approximately 2.6 times the magnitude of the secondcurrent.
 14. The method of claim 11, wherein the magnitude of the firstcurrent is between approximately 1.5 and 3.5 times the magnitude of thethird current.
 15. The method of claim 14, wherein the magnitude of thefirst current is approximately 1.6 times the magnitude of the thirdcurrent.
 16. The method of claim 11, wherein providing a first currentto produce a corresponding first color of light comprises applying thefirst current to a red emission area of the device so as to produce redlight.
 17. The method of claim 16, wherein providing a second current toproduce a corresponding second color of light comprises applying thesecond current to a green emission area of the device so as to producegreen light.
 18. The method of claim 17, wherein providing a thirdcurrent to produce a corresponding third color of light comprisesapplying the first current to a blue emission area of the device so asto produce blue light.
 19. The method of claim 11, further comprisingemitting the first, second and third colors of light through a polarizerincluding a colored substance corresponding to one of the first, secondor third colors of light.
 20. The method of claim 19, wherein thepolarizer includes a red colored substance configured to increase atransmission of red light.
 21. The method of claim 19, furthercomprising selecting the colored substance based on a pixel color of thedevice which requires the highest current to produce a given level ofbrightness.